The present invention relates generally to devices and methods for monitoring patient activity, and particularly to means for detecting the movement of a patient in a bed from a horizontal, i.e. prone or supine position to an erect or semi-erect position, as in an attempt by the patient to get out of bed preparatory to ambulation.
It is often desirable to ensure that hospital patients remain supine or keep to their beds, especially after and while recovering from surgery, and when bed rest is absolutely required. It is also often desirable for hospital personnel to directly monitor the physical activity of a patient without actually being in attendance at the patient's bedside, so as to be aware of any activity which may be deleterious to the patient's condition. Thus, it is often desirable to monitor a patient in order to detect, and therefore be able to avoid, the anesthetized patient, as upon partially regaining consciousness after coming out of surgery, getting out of bed (or making an attempt to do so) when such activity may place the patient, who may not be aware of his/her own condition, at risk. At the same time, the use of restraints is undesirable, for obvious reasons, making it necessary for attending personnel to personally monitor the patient's activity level in order to assure the patient does not make or undertake any movement which might jeopardize the patient's condition. Typically, it might be desired to guard against the patient getting out of bed, however such might not be detected by hospital personnel until the patient has actually done so. Thus, it is desirable for hospital personnel to be able to detect when the patient is attempting to, or in the process of alighting the bed preparatory to patient ambulation, and to alert the hospital personnel of this impending activity, so as to permit the hospital personnel to attend the patient before alighting and ambulation actually proceed. The present invention is directed to a means for making possible such early detection of patient movement indicative of impending patient ambulation.
More particularly, the present invention is directed to a device which attaches easily and unobtrusively to a lateral surface of the thigh or other portion of the body of a patient and which is sensitive to attitudinal changes in the orientation of the patient's thigh or body so that an alarm signal is produced thereby when the patient attempts to step out of bed preparatory to ambulation, this alarm signal preferably being transmitted over the "nurse's call" system for alerting attending health care personnel of the patient's activity. Additionally, the device provides an alarm signal if it is removed or becomes dislodged from the patient. Advantageously, the alarm signal remains on until reset at the device, in distinction to a normal nurse call signal which may be cancelled at the nurse's station console, thus indicating to attending personnel that the alert signal is from the patient ambulation motion detector device and not simply a nurse call signal.
The patient ambulation detector device of the present invention is self-attaching and is adapted for attachment to either the right or left thigh or to the upper body of the patient as appropriate. The device is compact, simple in construction and relatively inexpensive to manufacture. Further, the device can be easily connected to existing nurse call systems, without electrical or mechanical system modification.
A number of devices for monitoring bed-patient movement have been previously proposed. One such device is disclosed in U.S. Pat. No. 4,536,755 of Holzgang et al., and includes a mercury switch mounted on a circuit board and constituting an angle inclination sensing means for sensing angular displacement of a patient's upper leg relative to a reference datum plane. In this prior device, the circuit board with the mercury switch mounted thereon is housed in an enclosing carrier module which is strapped to the patient's thigh by means of an elastic band so as to be positioned on the anterior, i.e. upper surface of the patient's thigh, i.e. femur. An adhesive-backed foam pad is attached to the rear wall of the carrier module to serve as an interface between the patient's thigh and the module, to secure the device in place without detriment to patient comfort. In order to detect the unauthorized removal of the device from the patient's thigh, the device also includes a pressure switch having contacts which project from the lower surface of the circuit board and extend through an aperture in the carrier module rear wall to engage the anterior surface of the patient's thigh. Sensing of the downwardly directed angular inclination of the distal end of the patient's femur is accomplished by orienting the mercury switch on the circuit board so that, when the device is secured to the patient's thigh, an upwardly or downwardly directed angular inclination of the femur portion of the patient's leg proximal the knee has the effect of adjusting the position of the mercury contained in the switch. In this way, a downwardly directed inclination of the patient's leg which exceeds a preselected inclination threshold angle will bring the mercury within the switch casing into contact with a pair of respective electrodes to form a closed conduction path therebetween, effecting closure of the switch and applying battery voltage to a time delay circuit and thence to the gate electrode of an SCR, thereby switching the SCR on. When switched on, the SCR supplies current to an alarm circuit oscillator stage which generates audio frequency tone bursts which are applied to an audio transducer for producing an audible signal to indicate to attending personnel that the patient is in an "ambulatory enabling" position. Unauthorized removal or dislodgement of the device from the patient's thigh causes the pressure switch to close, which in turn causes immediate sounding of the audible alarm signal.
This prior device has only limited usefulness, for several reasons. Being battery powered, it is susceptible to becoming inoperative due to the battery running out. Additionally, the device only produces an audio alarm signal from the self-contained audio transducer, which alarm signal may not be audible to hospital personnel located, for example, at a nurse's station some distance from the patient's room, especially if the door to the patient's room is closed. Further, the audio alarm may not be audible above or distinguishable from background and other noise, such as paging messages, in the hospital ward. It is suggested that a radio transmitter might be substituted for the audio transducer to produce an inaudible warning signal for reception at a remote location. However, such a system is still susceptible to inoperability due to a partially or completely discharged battery, and requires the additional expense of installing reception means at each necessary location for alerting the responsible attending personnel.
Another prior device of this type which utilizes a specially configured mercury switch position sensor is disclosed in U.S. Pat. No. 4,348,562 to Florin. This disclosed device is described to provide an alarm system which is capable of being integrated with existing hospital call systems so as activate a patient's call light and/or buzzer, thereby notifying the nurse of the exact location of the patient at risk. Such integration with existing call systems would be advantageous also in that no additional power supply would be required.
This prior device monitors changes in position from the horizontal of the anterior surface of a patient's chest or thigh towards a more vertical orientation which may signify impending injury due to a fall or rising of the patient. The device uses a particularly configured special mercury switch casing designed with a large head chamber, in which a mercury ball normally resides, connected via an axial throat passage to a smaller foot chamber wherein are provided spaced-apart electrodes. Basically, the head chamber and its transition region with the connecting throat passage are so configured as to prevent the mercury passing into the throat passage until the angle of inclination of the anterior body surface of the patient to which the device is attached exceeds 70.degree. from the horizontal, while the foot chamber is made deep, so that once the mercury has moved down into the foot chamber and switch closure has thereby been effected the mercury is prevented from flowing back out of the foot chamber into the throat passage and opening the switch until the switch assembly is inverted to a 90.degree. head-down position for thus resetting the device.
This described prior device is fashioned by forming the chambers and connecting passage in a plastic block into which are led connecting wires the ends of which are bared and particularly disposed in the foot chamber for providing the switch contacts, with closure lids being fastened atop and below the block. A removable adhesive is applied to the bottom surface of this assembly in order to prepare it for application to an anterior horizontal surface of the patient. However, this prior device also has limited usefulness, due in part to the cost and complexity of fabricating the specially configured chambers and connecting passage. Also, both this prior device of Florin and the previously noted prior Holzgang et al. device are both required to be positioned on an anterior surface of the patient's body for obtaining therefrom a horizontal plane datum, and are consequently obtrusive. Further, in practice the disposition of the anterior surfaces of a patient's body may not in fact lie on the horizontal but rather may tend to be more or less inclined when the patient is lying in bed, and will naturally tend to move inclinedly along with normal body movements as during breathing. Also, it may be the case that portions of the patient's body, and hence its anterior surfaces, are intended to be inclined or reclined for various reasons such as to promote drainage, assist respiration or maintain traction or flexure, in which case a monitoring device which necessarily requires attaching at an anterior horizontal body surface may not be at all suitable.
The sensing of the patient's physical position and movement with an ordinary gravity mercury switch used as a motion detector is advantageously convenient, as ordinary mercury switches are small, sensitive and widely available at reasonable cost. However, when a mercury switch type device is designed to be attached or positioned on an anterior, i.e. horizontal portion of the supine patient's body, it become necessary to orient the ordinary mercury switch itself generally vertically inclined or upright in order to be sensitive to vertical inclination movement relative the horizontal datum plane, and thus the device enclosure must be made sufficiently large to accommodate the height of the generally vertically oriented mercury switch bulb, making the device bulky and obtrusive, or a specially configured custom mercury switch must be utilized as in the noted Florin device having the mercury switch in a generally horizontal disposition, in order to obtain a lower height aspect while remaining insensitive to normal slight motion about the horizontal datum.
Other prior devices for monitoring patient movement or for providing an alarm upon impending vacating of the bed by the patient are known from U.S. Pat. Nos. 4,179,692 to Vance; 4,583,084 to Henderson et al.; and 4,633,237 to Tucknott et al.
The present invention, in accordance with a first embodiment, provides a patient ambulation motion detector device of the mercury switch type which overcomes the limitations of the conventional devices, and which is unobtrusively positionable on a lateral surface of the patient's body, whereby it is made possible to utilize a generally vertically inclined ordinary mercury switch in such a device for reliable detection of patient body motion relative the horizontal datum plane. According to the first embodiment, the present invention provides a patient ambulation motion detector of the mercury switch type which is of simple design, having only three electrical components, one for sensing patient motion, one for detecting detachment of the device and one serving for mounting and interconnecting the other two, and which is connectable to conventional hospital nurse call systems.
According to a second embodiment, the present invention provides a motion detector having three motion single pull/single throw (SPST) detection mercury switches. The three mercury switches are electrically connected in series and each is arranged in a predetermined geometric orientation so as to minimize false alarms. Specifically, a centrally mounted switch detects relative vertical position and two adjacently mounted switches are provided to prevent unwanted alarm activation caused by the patient rolling over in bed to either side.
The above and other objects and advantages of the present invention will become more readily apparent from the following detailed description taken with reference to the accompanying drawings.